Stability of relativistic jets from rotating, accreting black holes via fully three-dimensional magnetohydrodynamic simulations

Abstract

Rotating magnetized compact objects and their accretion discs can generate strong toroidal magnetic fields driving highly magnetized plasmas into relativistic jets. Of significant concern, however, has been that a strong toroidal field in the jet should be highly unstable to the non‐axisymmetric helical kink (screw) m= 1 mode leading to rapid disruption. In addition, a recent concern has been that the jet formation process itself may be unstable due to the accretion of non‐dipolar magnetic fields. We describe large‐scale fully three‐dimensional global general relativistic magnetohydrodynamic simulations of rapidly rotating, accreting black holes producing jets. We study both the stability of the jet as it propagates and the stability of the jet formation process during accretion of dipolar and quadrupolar fields. For our dipolar model, despite strong non‐axisymmetric disc turbulence, the jet reaches Lorentz factors of Γ∼ 10 with opening half‐angle θj∼ 5° at 103 gravitational radii without significant disruption or dissipation with only mild substructure dominated by the m= 1 mode. On the contrary, our quadrupolar model does not produce a steady relativistic (Γ≳ 3) jet due to mass loading of the polar regions caused by unstable polar fields. Thus, if produced, relativistic jets are roughly stable structures and may reach up to external shocks with strong magnetic fields. We discuss the astrophysical implications of the accreted magnetic geometry playing such a significant role in relativistic jet formation, and outline avenues for future work.

PROBING THE INNERMOST REGIONS OF AGN JETS AND THEIR MAGNETIC FIELDS WITH RADIOASTRON. I. IMAGING BL LACERTAE AT 21 μas RESOLUTION

“…These are produced by dynamically important magnetic fields twisted by the differential rotation of the black hole's accretion disk or ergosphere (Blandford & Znajek 1977;Blandford & Payne 1982;McKinney & Blandford 2009;Zamaninasab et al 2014). Observational signatures for the existence of such helical magnetic fields can be obtained by looking for Faraday rotation gradients, produced by the systematic change in the net line-of-sight magnetic field component across the jet width (Laing 1981;Asada et al 2002).…”

The stability of astrophysical jets

“…The propagation, radial structure and growth or damping of instability produced jet structures depends on whether the structure is magnetically (CDI) or kinetically (KHI) induced. Non-relativistic and relativistic simulations of magnetized jet formation and/or propagation have shown helical structures attributed to CDI, e.g., ; Nakamura et al (2001); Ouyed et al (2003); Nakamura & Meier (2004); Nakamura et al (2007); Moll et al (2008); Moll(2009);McKinney & Blandford (2009);Carey & Sovinec (2009). Non-relativistic and relativistic simulations of kinetically dominated jets have shown that helical structures may be attributed to KHI, e.g., ; Hardee et al (2001); Hardee & Hughes (2003).…”

“…The 3D relativistic jet generation simulation performed by McKinney & Blandford (2009) indicates relatively rapid, less than 25 gravitational radii, but non-disruptive kink development over 500 gravitational radii. Our simulations for static and moving kinks suggest that the non-disruptive kink development in the jet generation simulation could be a result of the velocity shear surface located less or on order of the characteristic magnetic radius and a transverse density increase.…”

Jet Signatures in the Spectra of Accreting Black Holes

“…For our non-MAD model, we use the dipole model of McKinney & Blandford (2009). In this simulation, a MAD state does not develop and the accretion is driven by the magneto-rotational instability.…”